Dentin is a portion of the tooth internal to the enamel and cementum that has a radially striated appearance owing to a large number of fine canals or tubules known as the dentinal tubules. Tubules run from the pulp cavity to the periphery of the dentin and are generally about two microns in diameter at their base and somewhat narrower at their periphery. Tubules are not usually exposed to the environment in the oral cavity, as they are usually covered by enamel or cementum. The cementum in turn is often covered by the gums.
It is commonly understood that partially or fully exposed tubules can lead to tooth sensitivity, an irritating and painful condition. In this theory, recession of the gum line exposes cementum to erosion. The eroded cementum in turn exposes the hollow dentinal tubules. The exposed tubules cause nerves within the tooth to be affected excessively by external oral stimuli because material and energy transfer between the exterior and interior of the tooth is accelerated through the tubules. Common environmental stimuli, such as heat, cold, chemicals and physical and mechanical pressure or stimuli, such as brushing, are able to irritate the nerve through the open dentin tubules and thereby create pain. The pain of sensitive teeth appears to result from these stimuli, which apparently cause fluid movements in the dentinal tubules that activate pulpal nerve endings.
Conventionally, two approaches have been taken to treat or ameliorate tooth sensitivity. Under one approach, the chemical environment proximal to the nerve is altered by application of various agents, such that the nerve is not stimulated, or not stimulated as greatly. Known agents useful in this chemical approach, including potassium salts (such as potassium nitrate, potassium bicarbonate, potassium chloride) and strontium, zinc salts, and chloride salts.
The second approach involves the mechanical shield of the nerve by, e.g., blocking of the dentinal tubules wholly or partially with “tubule blocking agents.” Agents that have been disclosed in the prior art include, e.g., cationic alumina, clays, water-soluble or water-swellable polyelectrolytes, oxalates, amorphous calcium phosphate, hydroxyapatite, maleic acid copolymers and polyethylene particles.
US-A1-2009/0186090 in the name of the present Applicant discloses the provision of an oral care composition that reduces and/or eliminates the perception of tooth sensitivity. The composition includes an adherent material and includes, in part, silica particles having a particle size of 2-5 microns.
However, even though such an oral care composition provides clinical hypersensitivity relief, there is nevertheless still a need in the art for an oral care composition, in particular a dentifrice, that, upon use, provides enhanced prevention or reduction of tooth sensitivity and is not associated with significant processing or formulation disadvantages.
It is also known is the art to use zinc oxide as an antiplaque/anticalculus agent. It is also known to use complexes of divalent or trivalent metal ions as antiplaque agents.
It has been demonstrated in the literature that the solubility of zinc can be improved by forming a complex with a chelating molecule such as ethylenediamine tetraacetic acid or a bioactive molecule such as a cyclic alpha-hydroxyketone. For example, as disclosed in U.S. Pat. No. 6,287,541, specific cyclic alpha-hydroxyketones are used as complexing agents for divalent copper, zinc, iron or tin and trivalent iron S. Y. Gan, et al. “Antibacterial Activity of Zn-chelator Complexes.” IADR, March 2009 discloses the use of inert biocompatible chelators for zinc.
However, increased solubility does not guarantee an increase in anti-plaque, anti-gingivitis, hypersensitivity, and/or fresh breath efficacy. To provide these benefits the zinc must be delivered to the hard and/or soft tissues in the oral cavity.
There is still a need for enhanced delivery of antiplaque/anticalculus agents to the oral surfaces, in particular hard and/or soft tissue in the oral cavity.